[13] RFR: JDK-8215567: Change JavaFX release version to 13

[Kevin Rushforth]

Hi Phil or Johan,

Please review the following to bump the JavaFX release version to 13, 
now that we have forked the 12-dev stabilization repo:

https://bugs.openjdk.java.net/browse/JDK-8215567
http://cr.openjdk.java.net/~kcr/8215567/webrev/

Thanks.

-- Kevin